Cementitious articles, such as gypsum board and cement board, are useful in a variety of applications, some of which require a degree of water resistance. Traditional paper-faced cementitious articles do not always perform well under high moisture conditions, or upon exposure to the outdoors. Thus, for such applications, it is often desirable to use a cementitious article that is faced with a glass or polymer-based fiber mat instead of paper. It also is advantageous to use additives in the cementitious core that improve the water resistance of the core material itself.
The manufacturing process of cementitious articles, such as gypsum board and cement board, typically involves depositing a cementitious slurry over a first facing material and covering the wet slurry with a second facing material of the same type, such that the cementitious slurry is sandwiched between the two facing materials. Thereafter, excess water is removed from the slurry by drying. The cementitious slurry is allowed to harden to produce a solid article prior to final drying.
The manufacturing process of cementitious articles, thus, often requires the facing material to be sufficiently permeable that excess water can be removed from the cementitious slurry in the drying process. For example, non-woven fiberglass mat is often used as a facing material, in which the space between the fibers provides permeability. The permeability of the fibrous facing materials, however, makes the manufacturing process more difficult because the cementitious slurry deposited on the fibrous mat facing material tends to penetrate the mat causing slurry build-up on the forming table and assembly line. The slurry build-up must be removed periodically. Increasing the viscosity of the slurry can reduce the amount of slurry that penetrates the fibrous mat facing material, but the required higher viscosity is not always optimum for use in existing plant production processes due, for instance, to changes in mixing, setting, drying, or hardening characteristics.
Furthermore, the permeability of the fibrous mat facing material also reduces the water-resistance of the cementitious article because it allows water to penetrate the mat and contact the cementitious core during use. In order to alleviate this problem, exterior coatings of hydrophobic resins are sometimes applied. However, this generally requires an additional post-manufacturing step to be employed, adding cost and inconvenience.
Another approach is to further increase the water resistance of the cementitious core material by including hydrophobic additives in the cementitious slurry. A preferred additive for this purpose is a siloxane oil. However, methods of employing such additives require further improvement in their implementation and effectiveness.
Thus, there remains a desire for new water resistant cementitious articles, as well as methods of preparing such articles.